The invention relates to a diagnostic system for a valve that can be actuated by a position controller via a drive with a device for recording, storing, and evaluating, structure-born noise spectra on the valve. The invention also relates to a method for diagnosing the state of a valve.
In such a diagnostic system, known from European Patent EP 0 637 713 A1, a structure-borne noise sensor, the signal of which is supplied to a device for recording and storing structure-born noise spectra, is mounted to the housing of the valve. In an intact valve and a defective valve, there are different characteristics of the vibration level over a certain frequency. By forming the surface integral, and defining an acceptable deviation, it is possible to detect a defective valve. In particular, it is possible to determine wear caused by corrosion, cavitation, or erosion.
One object of the invention is to permit a particularly reliable diagnosis on valves.
According to one formulation of the invention, these and other objects are solved by a diagnostic system of the initially defined type, wherein a structure-born noise spectrum, which is recorded when an intact valve is slightly open, is stored in a device for recording, storing, and evaluating. Then, the valve is closed for diagnostic purposes, and a structure-bome noise spectrum is recorded. Then, the similarity between the recorded structure-bome noise spectrum and the stored structure-bome noise spectrum is used as a criterion for evaluating valve leakage.
The structure-borne noise spectrum of defective valves depends not only on the valve itself, but also on the medium flowing through it, the pressure of this medium, and the background noise during normal operation, e.g., the noise of adjacent pumps. As a result, the structure-bome noise spectra of an intact and a defective valve cannot be determined exactly in advance. In its almost closed position, however, a valve produces a structure-borne spectrum that is very similar to a closed valve with a defective valve seat. In the diagnostic system according to the invention, the structure-bome noise spectrum that is recorded in the almost closed, or slightly open, valve and then stored is therefore used as a reference to identify the structure-bome noise spectrum of a closed valve with a defective valve seat.
Conversely, to be able to identify the structure-bome noise spectrum of a closed valve with an intact valve seat, an additional structure-bome noise spectrum that is recorded in a closed intact valve is stored in the device for recording, storing, and evaluating. The similarity between the structure-borne noise spectrum recorded in the valve closed for diagnostic purposes, and the additional stored structure-borne noise spectrum is used as a criterion for evaluating the intactness of the valve.
The different criteria for the leakage of the valve and the tightness of the valve can be linked to a valve state signal, preferably by fuzzy linkage.
Since the operational background noise that enters into the structure-borne noise spectra, e.g., pump noise, can differ depending on when the structure-borne noise spectra are recorded, it is provided that when the structure-borne noise spectrum for a defined valve position is recorded, an additional structure-borne noise spectrum in another valve position also is recorded. Then, prior to the recorded structure-borne noise spectrum being stored and/or evaluated, corresponding spectral componentsxe2x80x94between the additionally recorded structure-borne noise spectrum and the recorded structure-borne noise spectrumxe2x80x94are removed from the recorded structure-borne noise spectrum. The structure-borne noise spectra that are being stored, or are to be evaluated, are then essentially independent from random momentary background noise.
The device for recording, storing, and evaluating, structure-borne noise spectra is preferably an integral component of the position controller, so that the diagnosis of the valve can be prompted via the data interface of the position controller, and so that the result of the evaluation can be checked via this data interface.